The following discussion of the background art is a result of the present inventors analysis of the systems and features of searchlight technology of the background art. The present invention relates to limitations on a flight crew's ability to see areas outside the aircraft, such as areas that are blocked by the aircraft's structure. Aircraft generally have landing lights mounted thereon to provide illumination during taxi, take-off, and landing when visibility is reduced by darkness or adverse weather conditions.
Landing lights may be mounted in a fixed position on the aircraft. Alternatively, the landing lights may be pivotable by a drive unit or device to extend from the aircraft when needed, and retracted to reduce drag when not in use. Searchlights are pivotable by a drive device similar to landing lights, but include an additional capability to rotate up to 360 degrees in a plane perpendicular to the extend-retract plane. Military and law enforcement helicopters commonly use searchlights to aim a beam of light in a desired direction to illuminate targets.
With the advent of infrared based Night Vision Imaging Systems (“NVIS”) for covert operations, a need has arisen for landing lights and searchlights that are compatible with NVIS by producing infrared light for illuminating the selected landing and search areas while eliminating visible light. Early NVIS-compatible landing and searchlights used infrared light filters installed over conventional visible lighting systems.
A disadvantage of early NVIS-compatible lighting systems was that the flight crew could not switch from visible to NVIS modes during a mission, since the infrared filters were required to be installed and removed while the aircraft was on the ground. This disadvantage was overcome by prior dual mode lightheads containing both visible and infrared lighting elements.
U.S. Pat. No. 5,695,272 to Snyder et al., the entirety of which is hereby incorporated by reference, describes an exemplary visible and infrared lighting element of the background art. Snyder et al. describes a lamp head having a visible light section and an infrared section. An operator is able to switch between infrared and visible light filaments controlled on a lamp head that may be extended, retracted and rotated through the use of relays and a mode selector switch.
Dual mode lightheads allow the flight crew to switch between visible and infrared lighting modes by simply applying electrical power to either the infrared or visible portions of the dual mode lighthead as desired. While prior dual mode lightheads offer significant advantages over early manually-installed filters, they suffer from several disadvantages. First, replacement of failed lamps is a cumbersome and difficult process owing to the segmented lens and filter assembly which must be removed and then re-sealed each time a lamp is replaced. This repair frequently causes damage to the reflectors, thereby reducing the optical efficiency of the lighthead.
In addition, dual mode lightheads typically emit lower light intensity than dedicated infrared or visible lighting systems, since the surface area on the lighthead available for the lighting system is divided between the visible and infrared portions. Further, prior dual mode lightheads utilize visible light sources coupled with infrared filters to produce the infrared light, generating high temperatures within the lighthead that can limit the life of the light elements, lenses, and sealing materials.
U.S. Pat. No. 5,589,901 to Means, the entirety of which is hereby incorporated by reference, describes an apparatus and method for synchronizing control of separate search and surveillance devices, e.g. a searchlight and an infrared and/or video camera can be directly linked electronically so that a user's movement and positioning of one of the devices directly determines the movement and positioning of the other device. However, this system requires a relatively complex comparator to permit the synchronized operation of the separate devices. Accordingly, the present inventors have determined that there is a need for a dual or multi-mode lighthead that is easier to maintain, provides higher intensity light output, and operates at a lower temperature to extend lighthead component life.